Known electric power converters are used in particular in uninterruptible power supplies, and speed variators for electric motors or associated with power generators for coupling to a distribution system. Such a converter 1 represented in FIG. 1 generally comprises DC voltage VDC lines L1 and L2 and an inverter 2 formed by power semi-conductor legs 2A, 2B, 2C connected between the lines L1 and L2 to supply AC voltages VO on output to a load 3 or to an electric power distribution system. When the legs are controlled in high frequency, in particular in pulse width modulation, electric filters 4 can be fitted between the outputs of the legs 2A, 2B, 2C and the load 3 or power system. A voltage and current measuring device 62 arranged on output lines 61 supplies signals Vo and Io to the control circuit. Often a rectifier 5 connected between AC inputs VI and the lines L1 and L2 supplies the DC voltage VDC. Capacitors C1 and C2 connected to the lines L1 and L2 perform filtering of the DC voltage VDC.
FIG. 2 shows an example of a part of a processing unit 7 of a control circuit 6 to supply control signals of the legs. In this circuit, a regulator 8 enables three-phase modulation signals to be regulated and supplied according to reduced setpoints Cd, Cq, Co, in particular by a Park or Concordia transform in the dqo or αβo domains. These known transforms and rotations are generally computed by means of matrices respectively called Park and Concordia matrices. Signals MC1 for each phase on output of the regulator are preferably used for intersective type modulation on a triangular high-frequency carrier signal enabling pulse width modulation. In the diagram of FIG. 2, the regulator 8 supplies first three-phase modulation signals MC1, a module 9 determines signals of general control component OM comprising an over-modulation to be applied to the first signals MC1 with operators 10, a module 11 applies a reference voltage V2 to said signals MC1 by operators 12, and a module 13 supplies a high-frequency signal designed to be modulated by modulation signals MC2 modified by the operators 10 and 12. Operators 14 combine the modulation signals MC2 with preferably triangular high-frequency signals F1 to supply control signals CVA, CVB and CVC of the inverter legs 2A, 2B, 2C in pulse width modulation format. As the leg controls are preferably binary on-off commands, a conditioning circuit 16 shapes the control signals. The over-modulation signals OM are generated by the modulation signals MC1 and by the type of over-modulation. The reference signal V2 is generally representative of a DC voltage, for example half of the voltage VDC of the lines L1 and L2.
In known converters, the module 9 determines signals of general control component OM according to modulation signals MC1 and to a signal representative of a phase shift, for example an angle or a cosine φ between an output voltage Vo and current Io. An example of a module 9, represented in FIG. 3, shows the use of a signal representative of phase shift to act on the lead or lag of the general control component signal. Output current Io and voltage Vo signals are applied to a module 20 to compute a signal representative of a phase shift which will be supplied to the module 9 for determining the general control component.
In known devices of the state of the art, the use of signals representative of a phase shift to determine the general control component does not enable efficient over-modulation management to be achieved. The phase shift signals are in fact no longer usable when the loads are not balanced and/or non-linear. A phase shift signal for all of the three phases leads to errors of appreciation. Furthermore the use of a phase shift signal no longer enables high-performance over-modulation to be applied if the current-voltage phase shift exceeds a certain value, for example an angle greater than ±Π/6.